1. Field of Invention
The present invention is related to semiconductor fabrication. More particularly, the invention is related to plasma processing during semiconductor fabrication.
2. Description of Related Art
In the fabrication of semiconductor based devices (e.g. integrated circuits or flat panel displays) layers of material may alternately be deposited onto and etched from a wafer or substrate surface (e.g., the semiconductor wafer or the glass panel). As is well known in the art, the etching of the deposited layer(s) may be accomplished by a variety of techniques, including plasma-enhanced etching. In plasma-enhanced etching, the actual etching of the wafer or substrate takes place inside a plasma processing chamber. During the etching process, a plasma is formed from a suitable etchant source gas to etch areas of the wafer or substrate that are unprotected by a mask, leaving behind the desired pattern.
There are two types of plasmas that are employed in plasma-enhanced etching, namely, confined plasmas and unconfined plasmas. Unconfined plasmas touch the plasma processing chamber walls and may contaminate the wafer or substrate by re-depositing atoms from the chamber walls on to the wafer or substrate. Typically, the plasma processing chamber walls are made of materials that are incompatible to the wafer or substrate. With confined plasma, there is little or no contamination since the plasma is stopped by some means from reaching the chamber walls. Thus, confined plasmas provide a level of cleanliness that is not provided by well-known unconfined plasmas.
In prior art systems plasma can be prevented from reaching the chamber walls by establishing a variety of repulsive fields, either electric or magnetic in nature. By way of example, the plasma is confined by a plurality of confinement rings resident within the chamber walls and by means of draining charge out of the plasma just before it can reach the inner limits of the confinement rings. Since the confinement rings are made from an insulating material they will charge to a potential comparable to that of the plasma. Consequently, a repulsive electric field will emanate from the leading edge of each confinement ring that will keep plasma from protruding any further out toward the chamber walls.
Referring to FIG. 1 there is shown an illustrative prior art system 100 having a process chamber that generates a capacitively coupled RF plasma. By way of example and not of limitation, the illustrative system is an EXELAN system manufactured by Lam Research Corporation. The illustrative system 100 includes a parallel plate plasma reactor such as reactor 100. The reactor 100 includes a chamber having an interior 102 maintained at a desired vacuum pressure by a vacuum pump 104 connected to an outlet in a wall of the reactor. Etching gas can be supplied to the plasma reactor supplying gas from gas supply 106. For example, a medium density plasma can be generated in the reactor by a dual frequency arrangement wherein RF energy from RF source. 108 is supplied through a matching network 110 to a powered electrode 112. The RF source 108 is configured to supply RF power at 27 MHz and 2 MHz. Electrode 114 is a grounded electrode. A wafer or substrate 116 is supported by the powered electrode 112 and is etched with plasma generated by energizing the etch gasses into a plasma state. A plurality of confinement rings 120a and 120b confine the plasma. Other capacitively coupled reactors can also be used such as reactors wherein RF power is supplied to both electrodes such as the dual frequency plasma etch reactor described in commonly owned U.S. Pat. No. 6,090,304, the disclosure of which is hereby incorporated by reference.
Referring to FIG. 2 there is shown a cross-sectional view of the interior 102 of the plasma processing chamber 100. The interior 102 includes confinement rings 120a and 120b. Although only two confinement rings are shown, any number of confinement rings may be provided. Within the interior 102 of plasma processing chamber 100, there is shown a powered electrode 122 on which is adapted to receive a wafer or substrate 124. The powered electrode 124 can be implemented with any suitable chucking system, e.g. electrostatic, mechanical, clamping, vacuum, or the like, and is surrounded by an insulator 126 such as a quartz focus ring. During etching, RF power supply 128 can communicate RF power having a frequency of about 2 MHz to about 27 MHz to powered electrode 122. Above wafer or substrate 124, there is disposed a grounded electrode 130, which is coupled to confinement rings 120a and 120b. Another grounded electrode 132 abuts the insulator ring 126 and is located near the powered electrode 122. In operation, RF power supply 128 communicates RF power to powered electrode 122 that is electrically coupled to grounded electrode 130.